Illuminated graphic displays and buttons for automotive applications, such as the controls for a heating, ventilating and air conditioning system (HVAC), often have backlit buttons, each of which identifies and controls a function of the system. Such backlit components have an incandescent light source which is positioned behind the button in order to make an insignia formed on the button visible in the dark, necessitating that the insignia be capable of receiving light from the light source. A common approach is to form buttons from a white translucent material or from a transparent plastic material which is painted white to form a white translucent layer over the transparent substrate. The buttons are then painted black to form an opaque black cover layer, which is then selectively lased away to expose a portion of the underlying white translucent substrate, which serves as the insignia.
The translucent or transparent nature of the button maximizes the transmission of light from the incandescent light source for night time viewing, while the white translucent material or layer contributes graphics whiteness by reflecting light, such that the insignia can be visible under natural lighting conditions during daylight hours.
A difficulty in the design of backlit displays is the attainment of an adequate lighting intensity level while avoiding different backlighting intensities between adjacent buttons, which would cause irregular illumination intensities within a display group. This is particularly true with buttons of a backlit display which, for cost and design efficiencies, share one or more light sources. In order to reduce the variability of lighting intensity, such displays often incorporate lightpipes for the purpose of distributing light equally among the buttons. Though much effort has been directed toward optimizing the capability of lightpipes, uniform backlighting of each and every button is very difficult due to size and location constraints. As a result, it is at times necessary to apply facets and painted patterns to lightpipes in order to increase the light intensity directed to relatively dim areas. In particular, reflectors and additional lamps have been required at times to enhance the light intensity. In contrast, excessively bright areas have been attenuated with the use of printed halftone patterns behind the individual insignia.
Another challenge of current backlighting technology is the desire to produce a backlighting effect having an aesthetically pleasing appearance. In particular, the conventional use of incandescent light sources often tends to contribute a yellowish-white color to the display, which in some applications may be undesirable or unappealing to an observer. Consequently, color appliques and light filters are often employed to alter the color of the lighting effect produced by the light source. Other known shortcomings include poor reliability and short service life of incandescent light sources, and the requirement to dissipate the considerable amount of heat which these light sources generate.
From the above, it can be seen that significant shortcomings exist in the current technology for light sources and the means by which the light produced is delivered to a display. Accordingly, it would be desirable if a backlighting system existed which was highly reliable and produced an aesthetically pleasing backlighting effect for a backlit display of an automobile. Furthermore, such a system would require a minimal number of light sources, yet produce minimal variability in backlighting intensity between backlit components of a display at reduced power levels and operating temperatures for a given desired backlighting intensity.